Bag House filtering systems commonly comprise a particle collection chamber into which air containing particles is directed in order to remove the particles therefrom. Normally provided are a plurality of filter bags extending into the particle collection chamber, each surrounding a clean air outlet, and are supported therein by suitable support cages. Air passes through the filter bags to the clean air outlets which make connection with a clean air discharge chamber. The filter bags may be arranged in any desired array but are normally located in straight line distributions within the particle collection chamber.
For filtering systems to work efficiently, it is necessary to repeatedly remove particle build up on the outside of filter bags, with the particles thus removed being collected and removed from a base zone of the particle collection chamber. One known arrangement for removing the aforesaid particle build up is to direct a reverse pulse of pressurised air which passes from discharge holes in a blow tube located within the clean air discharge chamber into the mouth of each filter bag. The reverse air pulse rapidly expands the bag to dislodge the particle build up. To increase the air flow in the reverse pulse it has also been proposed to use various forms of venturi arrangements on or adjacent to the mouth of the filter bag. In one known arrangement of this kind, the venturi provided extends into the top section of the filter bag.
Known cleaning arrangements of the aforementioned kind are believed to have a number of inefficiencies caused by differing factors. One such factor is apparently minor irregularities in the form of the discharge holes in the blow tube or tubes. Further, since a free air stream tends to expand conically, the reverse air pulse should be as accurately as possibly positioned coaxial with, and aligned with, the central axis of the filter bag. Misalignment can cause a greater effect on one side of the filter bag than the other with the ultimate effect being that one side of the filter bag may be over cleaned whilst the other may not receive any cleaning effect at all.
A still further inefficiency arises from the structure of bag house filter systems where a plurality of bag filters are supplied with cleaning air released into one end of a usual type of blow tube open at one end and closed at the other with discharge holes being located at spaced locations in line along the tube. Typically air flow volume and direction through the first discharge hole may be vastly different to air flow volume and direction through the last discharge hole from the air supply and of the blow tube. This causes significant differences in cleaning between the various bag filters supplied with reverse pulse cleaning air along the length of one blow tube.
Finally it has been recognised that in those arrangements where a venturi extends into a filter bag, zones of the filter bag adjacent to the venturi outlet will not have full cleaning effect from a reverse pulse air flow.
Variations in the uniformity of cleaning arrangements of the aforementioned kind have the effect of requiring increased filter bag filtering surface areas and/or increased levels of consumption of reverse pulse air flow. This has the effect of increasing the size and capital costs of any bag house filter installation as well as increasing operating costs (due in part to decreased bag life) because of the increased reverse pulse air flows.